Through extensive mutagenesis trial-and-error efforts, a stable, homodimeric construct of the catalytic core domain of the HIV1 integrase enzyme has been generated. Although under conditions that closely resemble the physiological environment the enzyme rapidly samples different conformational states, leading to extensive line broadening and disappearance of NMR signals, we have found conditions that include high Mg2+ concentrations (40 mM) where the equilibrium is shifted to what appear to be one major and one minor state, that differ from one another in the structure of the C-terminal helix. Analysis of relaxation data provides insights into the dynamic properties of the active site, which indeed shows considerable amplitude high frequency motions, but shows a continuation of the helix preceding this site well beyond what is seen in many X-ray structures.